The subject matter disclosed herein relates to gas turbines, and more specifically, to injectors for axial fuel staging in gas turbines.
In a gas turbine engine, combustible materials (e.g., fuel mixed with air) are combusted in a combustor, producing high-energy combustion fluids. The combustion fluids are directed to a turbine via a transition duct, where the combustion fluids aerodynamically interact with turbine blades, causing them to rotate. The turbine may be coupled to a compressor by one or more shafts such that the rotating blades of the turbine drive the compressor. The turbine may be used to generate electricity, power a load, or some other use.
Emissions (e.g., NOX emissions) of the gas turbine engine may be reduced by increasing the consumption of the combustible materials during combustion, resulting in a more complete combustion reaction. Injecting additional combustible materials into the combustion fluids as they pass through the transition duct (i.e., “axial fuel staging”) may increase the temperature and energy of the combustion fluids, and lead to a more ideal consumption of fuel, thus reducing emissions (e.g., NOX emissions).
Turning now to the figures, FIG. 1 is a block diagram of an embodiment of a turbomachine system (e.g., gas turbine engine 10). The gas turbine engine 10 may use liquid and/or gas fuel to drive the gas turbine engine 10. The fuel may be any suitable gaseous or liquid fuel, such as natural gas, liquefied natural gas (LNG), syngas, associated petroleum gas, methane, ethane, butane propane, biogas, sewage gas, landfill gas, coal mine gas, gasoline, diesel, naphtha, kerosene, methanol, biofuel, or any combination thereof. Fuel may be directed from one or more fuel supplies 12 to a combustor section 14. The fuel may be mixed with oxidant, such as air, at one or more points in the combustor section 14. The oxidant-fuel mixture combusts in one or more combustors 16 (e.g., combustor cans) of the combustor section 14, thereby creating hot pressurized combustion gases.
In some embodiments, the gas turbine engine 10 may include combustors 16 disposed about a shaft 18. Each combustor 16 may direct combustion gases into a turbine 20, which may have one or more stages 22, toward an exhaust outlet 24. Each stage 22 may include a set of blades coupled to a respective rotor wheel, coupled to the shaft 18. As the combustion gases cause rotation of turbine blades, the shaft 18 rotates to drive a compressor 26. Eventually, the gas turbine engine 10 exhausts the exhaust gases through the exhaust outlet 24.
One or more stages 28 of the compressor 26 compress the oxidant (e.g., air) from the oxidant intake 30. The one or more stages 28 may be coupled to the shaft 18. Each stage 28 includes blades that rotate to increase the pressure and to provide compressed oxidant. As the blades within the compressor 26 rotate, oxidant is drawn from an oxidant supply 32.
The compressed discharge oxidant from the compressor 26 is directed into one or more combustors 16 in the combustor section 14 to mix with the fuel. For example, fuel nozzles of the combustor section 14 may inject fuel and compressed oxidant into the combustors 16 in a suitable ratio for combustion. For example, suitable combustion may substantially completely combust the fuel with minimal emissions.
The shaft 18 may also be coupled to a load 34, which may be a mobile or a stationary load, such as a propeller on an aircraft or an electrical generator in a power plant. The load 34 may include any suitable device capable of being powered by the rotational output of the gas turbine engine 10.
FIG. 2 is a schematic of an exemplary combustor 16. The combustor has a head end 50, where fuel from the primary fuel supply 12 is mixed with air from the compressor 26. The fuel/air mixture is combusted in a first combustion zone 52. The fluids then travel down the combustor 16 to a transition duct 54, which includes a second combustion zone 56. The transition duct 54 may include a plurality of axial fuel staging (AFS) injectors 58 in one or more axial planes (injectors 58 being located in two planes in FIG. 2) and distributed circumferentially about the transition duct 54. However, AFS may also be applied to a combustor liner and transition duct combination, or a unibody combustor. The AFS injectors inject a second fuel from a secondary fuel source 60, mix the second fuel with compressed air from a compressed air source 61 (e.g., compressor 26), and inject the mixture in a direction that is generally transverse to the predominant flow direction 62. The second fuel and air mixture may combust in the second combustion zone 56. In some embodiments, the secondary fuel may be provided from a secondary fuel supply 60, in which case the secondary fuel or fuels may be more volatile than the primary fuel (e.g., any suitable gaseous or liquid fuel, such as natural gas, liquefied natural gas (LNG), syngas, associated petroleum gas, methane, ethane, butane propane, biogas, sewage gas, landfill gas, coal mine gas, gasoline, diesel, naphtha, kerosene, methanol, biofuel, or any combination thereof). In some embodiments, the secondary fuel may be the same fuel as the primary fuel and may be provided from the primary fuel supply 12. Injecting a second fuel/air mixture in the transition duct 54, as well as the head end 50, helps to encourage more complete combustion, which may reduce certain emissions (e.g., NOX emissions).
FIG. 3 shows a perspective section view of the transition duct 54, with AFS injectors 58 disposed circumferentially 40 about the transition duct 54. Such injectors 58 may be the same or similar to those described in commonly assigned U.S. patent application Ser. No. 13/233,127, the disclosure of which is incorporated by reference herein. As can be seen in FIG. 3, the AFS injectors 58 are “slotted” in that they are longer in the axial direction 36 than they are wide (in the circumferential direction 40). Compressed air from the compressor 26 is passed through each AFS injector 58. Each AFS injector 58 then injects the secondary fuel into the flow path of the compressed air through orifices. The slotted AFS injector 58 extends in the radial direction 38 through a reversed flow region or cooling sleeve and into the compressor discharge volume surrounding the combustor 16. The AFS injector 58 also extends in the axial direction 36, which is substantially aligned with the predominant flow path 62 through the transition duct 54. The AFS injector 58 also extends in the circumferential direction 40.
While the aforementioned injector systems for axial fuel staging may possess certain advantages, it would be desirable to further develop hardware and techniques for axial fuel staging to further increase combustible material consumption and reduce emissions in gas turbine engines. Such an objective is addressed by the present disclosure.